Field of the Invention
The present invention relates to a fuel cell assembly.
Description of the Prior Art
Fuel cells, especially those with a proton-conducting polymer film as a partition between the anode and cathode (proton exchange membrane (PEM) fuel cells), are operated on the anode side with a fuel gas, such as gaseous hydrogen, or gas mixtures containing hydrogen, such as reformate gases.
To improve the efficiency of such fuel cells, it is known to return the residual gas, leaving the anode side of the fuel cell on the outlet side, to the anode inlet side by means of so-called recirculation provisions or paths of the fuel cell. However, since in operation the fuel cell consumes only pure fuel, as a rule hydrogen, such recirculation of the fuel flow causes the concentration of pure fuel in the anode region of the fuel cell to decrease over the course of operation.
This is due to the accumulation of residual gases in this circulation loop, that originate either in the fuel gas supply or from diffusion from the cathode side, or in other words the side of the fuel cell supplied with air, and reach the anode side. This primarily involves nitrogen and water vapor. Because of the contrary or counterflow behavior the residual gas contact rises, and the proportion of pure fuel in the fuel cell drops, and the electrical voltage of the fuel cell drops as well. Increasingly, with high fuel gas consumption, the dynamics of the gas transportation to the proton exchange membrane (PEM) are slowed down.
To avoid high accumulations of residual gases in the anode region of the fuel cell, it is therefore known to cause the gas emerging from the anode region of the fuel cell to be vented to the environment, either permanently via a throttle restriction, or in a different embodiment, at regular time intervals via a suitably triggered valve. Such valves are known for instance by the term “purge valve”.